A known approach to microscopy utilising x-rays is projection x-ray microscopy, in which a focussed electron beam excites and thereby generates a spot x-ray source in a foil or other target. The object is placed in the divergent beam between the target and a photographic or other detection plate. There have more recently been a number of proposals for using the electron beam of an electron microscope to excite a point source for x-ray microscopy. Integration of an x-ray tomography device directly into an electron microscope was proposed by Sasov, at J. Microscopy 147, 169, 179 (1987). Prototype x-ray tomography attachments for scanning electron microscopes using charge coupled device (CCD) detectors have been proposed in Cazaux et al, J. Microsc. Electron. 14, 263 (1989), Cazaux et al, J. Phys. (Paris) IV C7, 2099 (1993) and Cheng et al X-ray Microscop) III, ed. A. Michette et al (Springer Berlin, 1992), page 184. Ferreira de Paiva et al (Rev. Sci. Instrum. 67(6), 2251 (June 1996)) have developed and studied the performance of a microtomography system based on the Cazaux and Cheng proposals. Their arrangement was an adaptation of a commercially available electron microprobe and was able to produce images at around 10 .mu.m resolution without requiring major alterations to the electron optical column. The authors concluded that a 1 .mu.m resolution in tomography was feasible for their device. All system components and methods of interpretation of image intensity data in these works were based on the mechanism of absorption contrast.
A review article by W. Nixon concerning x-ray microscopy may be found in "X-rays: The First Hundred Years", ed. A Michette & S. Pfauntsch, (Wiley, 1996, ISBN 0.471-96502-2), at ps 43-60.
The present applicant's international patent publication WO 95/05725 disclosed various configurations and conditions suitable for differential phase-contrast imaging using hard x-rays. Other disclosures are to be found in Soviet patent 1402871 and in U.S. Pat. No. 5,319,694. Practical methods for carrying out hard x-ray phase contrast imaging arc disclosed in the present applicant's co-pending international patent publication WO 96/31098 (PCT/AU96/00178). These methods preferably involve the use of microfocus x-ray sources, which could be polychromatic, and the use of appropriate distances between object and source and object and image plane. Various mathematical and numerical methods for extracting the phase change of the x-ray wavefield at the exit plane from the object are disclosed in that application and also in Wilkins et al "Phase Contrast Imaging Using Polychromatic Hard X-rays" Nature (London) 384, 335 (1996) and our co-pending international patent application PCT/AU97/00882. The examples given in these references primarily related to macroscopic objects and features, and to self contained conventional laboratory type x-ray sources well separated in space from the sample.
It is an object of the present invention, at least in a preferred application, to facilitate x-ray phase contrast imaging of microscopic objects and features.